The overall major aims of this project include studies on the mechanism of action and the mechanism of termination of activity of gonadotropins (human choriogonadotropin and luteotropin) in transplantable rat Leydig tumor cells. The binding characteristics of the hormones to the cells will be determined, and the steroid profiles of both unstimulated and gonadotropin-stimulated cells will be measured. The effects of (medium) cholesterol and lipoprotein levels on steroids-genesis will be determined; these studies will involve the use of inhibitors such as amino-glutethimide and cyanoketone. Experiments will be conducted to ascertain if the specifically bound gonadotropin is invaginated and degraded by the tumor cells; preliminary evidence indicates this to be the case. Concomitantly, the fate of the hormone receptor will be determined. These particular investigations are important in elucidating the mechanism of regulation of functional receptors by gonadotropins. An attempt will be made to establish the tumor cells in continuous culture. Lastly, it is proposed to initiate feasibility studies on the tumor cells as a potential source for the isolation of gonadotropin receptors.